Digital imaging and communication in medicine (DICOM) is a standard that specifies a nonproprietary data exchange protocol, which was developed by the American College of Radiology and the National Electrical Manufacturers Association. It has now become the uncontested standard for the exchange and management of biomedical images. Here, we hope to highlight the significance of DICOM in digital imaging and to illustrate its indispensable role in digital imaging in the future.

Digital imaging and communication in medicine (DICOM) is a standard that specifies a nonproprietary data exchange protocol which was developed by the American College of Radiology (ACR) and the National Electrical Manufacturers Association (NEMA). It aims to facilitate a common method of transmission for medical radiographic images. [1] In 1993, the current version (3.0) of DICOM was published by NEMA. The standard is developed by work groups every year to satisfy virtually any medical branch. [2]

DICOM Standard consisted of several layers in relation to ISO Open System Interconnection(OSI) network model. DICOM is independent of the physical layer because it does not define a physical connection. Upper layer protocol is defined inside the DICOM standard. It is an abstract protocol that defines data encapsulation and is higher than level five of the ISO OSI model. At the application layer there are five primary areas of functionality:

Transmission and persistence of complete objects (such as images, waveforms, and documents)

Query and retrieval of such objects

Performance of specific actions(such as printing images on film)

Workflow management(support of work list and status information)

Quality and consistency of image appearance(both for display and print). [2]

With this review article, we hope to highlight the significance of DICOM in digital imaging and to illustrate its indispensable role in digital imaging in the coming future.

Historical Aspect

Since the beginning of digital medical imaging, exchanging images between various kinds of equipment has been an issue. In 1985 and 1988, the ACR/NEMA standards were issued but did not provide a satisfactory solution. The publication of DICOM standard was followed by several demonstrations in key international congresses. In 1993, the whole community was convinced that the DICOM standard actually led to successful implementations. The manufacturers were willing to use it and turn the page of proprietary formats and solutions. In 1999, the position of DICOM was significantly reinforced with the creation of the DICOM Committee and the collaboration with other standards development organizations such as the Comité Européen de Normalisation in the mid-nineties and ISO TC 215 "health informatics." [3]

DICOM and DICOM file format have now became international and dynamic standard in the field of biomedical imaging. It is also being reviewed and modified on a regular basis. Dental input to this process comes from many organizations. American Dental Association (ADA) has been a member of the DICOM Standard Committee since 1996 and recommended as early as 2000 that dental manufacturers should make their files convertible to the DICOM file format. Those manufacturers who do not follow the DICOM standard will not be able to stay viable in a competitive marketplace. [4],[5]

The ADA Standards Committee on Dental Informatics (SCDI) also developed a Technical Report (TR) No 1023i: Implementation requirements to adapt the DICOM standards for the exchange of digital radiographic images in dentistry. [6] The DICOM requirements presented in the TR enable the exchange of digital radiographic images between dental providers regardless of operating systems. Dental digital imaging system vendors that follow the requirements should certify that they are in compliance with ADA SCDI TR 1023. [4] The influence of DICOM was critical in the emergence of multivendor technical solutions for picture archiving and communication systems (PACS), and in providing appropriate solutions for the integration with the other information systems involved, especially the hospital information systems and the radiology information systems. [3]

Recently, DICOM standard is used for handling, storing, printing, and transmitting information in medical imaging and also includes a file format definition and a network communications protocol. The communication protocol is an application protocol that uses TCP/IP to communicate between systems. DICOM enables the integration of scanners, servers, workstations, printers, and network hardware from multiple manufacturers into a PACS. DICOM has been widely adopted by hospitals and is making inroads in smaller applications such as dentists' and doctors' offices. [7]

Digital Imaging and Communication in Medicine and Teleradiology

"Teleradiology" should be defined as the formal transmission of images within a secure local area network instead of transmission by ordinary E-mail. E-mail transmission has disadvantages of not being able to secure nor are attached images diagnostic, particularly if they are loosely compressed. Teleradiology lacks standards for an interoperable, manufacturer-independent protocol for security reasons, and does not permit clients access to their images stored in the local area network's DICOM server. Tachibana and others designed a DICOM network-attached server (DICOM-NAS) that allows eligible clinical clients to access their images that are temporarily stored on the DICOM-NAS. Such temporary storage has greatly enhanced security. [8],[9],[10]

Advantages And Disadvantages of Digital Imaging and Communication in Medicine

DICOM has standardized the exchange of medical information and provided cost-effective interconnection of different medical systems. This has made the DICOM Standard stand in front of other separate standards developed by manufacturers of medical equipment and also helps in avoiding problems that occur if patient moves from one hospital to another. It supports all medical branches that make it so comprehensive, transparent, and easy to use. DICOM takes up less space for digital storage and digital data and is easy to transmit over a large geographical area. [11],[12]

Analog data in some cases suffer from quality degradation caused by limited durability of the media, and this is not the case with the digital data. Considering that problem DICOM offers a possibility to convert analog data to DICOM digital format, DICOM defines all the attributes that should be included in each modality. Those data fields can be required or optional.

A major disadvantage of the DICOM standard is the possibility for entering probably too many optional fields. This disadvantage is mostly shown in inconsistency of filling all the fields with the data. Some image objects are often incomplete because some fields are left blank and some are filled with incorrect data. Another problem occurs when displaying an image on a device that is made from different manufacturer, because different imaging equipment use different amplitude ranges and the same number of allocated bits. In that case, images can be displayed as underexposed or overexposed with poor contrast, so those parameters should be adjusted manually.

Role of Digital Imaging and Communication in Medicine in Cone-Beam Computed Tomography

Data transfer between workstations connected to a cone-beam computed tomography (CBCT) scanner also follows the DICOM standard protocol. The CBCT manufacturers provide software to generate DICOM files. There are wide ranges of softwares available to import DICOM files, work on them and export sections of images in other formats, and those images can later be used for various measurements. A major problem is, however, that the selection of parameters related to image generation and manipulation in CBCT imaging, including the selection of software, cross-sectional slice thickness, inter-slice interval, windowing (contrast control), and resolution, seems to have been performed almost arbitrarily. [13]

Appropriate use of information and communication technology (ICT) and mechatronic systems is considered by many experts as a significant contribution to improve workflow and quality of care in the operating room (OR). In addition, the development of standards to support the implementations of these new interventional tools must be carried out in parallel. The DICOM Working Group 24 "DICOM in surgery" has recently been founded to support the implementation of ICT systems in the digital OR. [14]

The first drawback to address is the contrast control of the displayed image or "windowing." For DICOM images, visualization is based on a threshold filter, which assigns a binary value, either transparent or visible, to each voxel based on its gray level value. For most DICOM orientation software, the user is able to define the critical value that splits the voxels into visible and invisible, or, in other words, the windowing of the image. This results in an image that is composed of all visible voxels. In 2011, Spin-Neto etal. stated that different windowing values provide different final images when different values for the center level (L) and bandwidth (W) of shades of gray are used. This may influence linear and volumetric measurements. [13]

Role of Digital Imaging and Communication in Medicine in Dentistry

Using DICOM compliant software interdisciplinary departments can link their communication such that pretreatment expectations equal posttreatment results. Finally, dental imaging centers staffed with board-certified oral and maxillofacial radiologists will become more commonplace, providing patient care that includes acquisition, interpretation, and conversion of DICOM data. In addition, oral and maxillofacial radiologists will be charged with educating the private practice dental community about the advantages of using DICOM data for better patient care. [4]

The development of the DICOM standard allowed to turn the page of proprietary standards for representing biomedical images and associated metadata. Initial efforts concerned primarily on the exchange and management of images acquired on imaging equipment. Image processing is now being considered as well with extensions of the standard dedicated to radiation therapy, computer-aided detection (CAD) structured reports, spatial registration, fiducial segmentation objects, and even more recently segmentation surfaces such as meshes. [3]

The future of diagnostic imaging using DICOM data is bright. Clinicians can import the DICOM data format into third-party software that serves as an adjunct in treatment planning. SimPlant (Materialize Dental NV, Leuven, Belgium) dental implant computer-guided software converts DICOM data into a file that provides information for presurgical planning. The software incorporates computer-aided design/computer-aided manufacturing replicas of dental implants for the clinician to place into the region of interest. The clinician sends the file to a manufacturing facility, which creates a surgical guide through a process termed "stereolithography." The guide includes metal cylinders that direct osteotomy drills into precise locations in the maxilla and/or mandible, as planned by the software. DICOM-compliant software known as "volumetric imaging software" is being used in orthodontics to merge photographic images with radiographic images so that clinicians can assess true soft- and hard-tissue relationships. Companies providing this technology include Anatomage (San Jose, California), Dolphin Imaging and Management Solutions (Chatsworth, California) and Materialize Dental NV. [4]

DICOM has started studying how processing tools, such as plug-in or web services, could be more easily shared in the future, based on standard application programming interfaces. This initiative, led by Working Group 23 "application hosting", received a strong support from the CaBIG initiative (Cancer Biomedical Informatics Grid) and the NCI, because of the perspectives it opens for in vivo imaging in cancer research, especially in molecular imaging and CAD. [3]

Conclusion

The DICOM standard has now become the uncontested standard for the exchange and management of biomedical images. Everyone acknowledges its prominent role in the emergence of multivendor PACS, and their successful integration with hospital information systems and radiology information systems, thanks to the Integrating the Healthcare Enterprise initiative. We introduce here the basic concepts retained for the definition of objects and services in DICOM, with the hope that it will help the reader to find his or her way in the vast DICOM documentation available on the web.